Attrition mill

ABSTRACT

An apparatus for the separation of fibers of cellulose pulp sheet material including an attrition mill having a stationary and an opposing rotary disc, the stationary disc having a central aperture for reception of sheet material, the apparatus further including an impact zone, a driven roll extending across the width of the sheet material for feeding the pulp sheet in unfolded state to the impact zone, a series of spaced hammers mounted in the impact zone on a driven shaft for hitting the sheet material adjacent to its leading edge, with repeated impact spaced across its width to break the pulp material at its leading edge into chips, the hammer elements adapted to coact in interfitting relation with a set of stationary spaced cutter teeth on a stationary bar, a series of spaced supporting elements staggered with respect to the hammers for supporting the sheet material adjacent to its leading edge, the construction being such that the chips fall between the spaced supporting members, a conveyor mounted below the supporting elements for receiving the chips and for continuously feeding the chips to the aperture.

United States Patent {72} Inventor CharlesR.Ly0n

Fort Mill, so. 211 Appl.No. 664,578 122 Filed June26, 1967 [73] AssigneeCelanese Corporation [54] ATTRlTlON MILL 5 Claims, 7 Drawing Figs. [52]U.S.Cl 241/152 [51] Int. Cl B02c 7/06, BOZc 13/06, B02c 21/00 [50] Fieldof Search 241/28, 29,

152,152(.5),157,158,160,186,247; 225/(lnquiry); 83/906 FORElGN PATENTS68,832 10/1891 Germany 241/152 I Primary ExaminerDonald G. KellyArt0rneysLeonard Horn, S. D. Murphy and Andrew F.

Saybo, Jr

ABSTRACT: An apparatus for the separation of fibers of cellulose pulpsheet material including an attrition mill having a stationary and anopposing rotary disc, the stationary disc having a central aperture forreception of sheet material, the apparatus further including an impactzone, a driven roll extending across the width of the sheet material forfeeding the pulp sheet in unfolded state to the impact zone, a series ofspaced hammers mounted in the impact zone on a driven shaft for hittingthe sheet material adjacent to its leading edge, with repeated impactspaced across its width to break the pulp material at its leading edgeinto chips, the hammer elements adapted to coact in interfittingrelation with a set of stationary spaced cutter teeth on a stationarybar, a series of spaced supporting elements staggered with respect tothe hammers for supporting the sheet material adjacent to its leadingedge, the construction being such that the chips fall between the spacedsupporting members, a conveyor mounted below the supporting elements forreceiving the chips and for continuously feeding the chips to theaperture.

Patented March 30, 1971 6 Sheets-Sheet 1 AWL INVENTUR CHARLES R. LYON)1? W 4 nrramr Patented March 30, 1971 3,512,595

6 Sheets-Sheet 2 INVENTOR CHARLES R. LYON er L ATTORNEY Patented March30,1971 3,512,595

' 6 Sheets-Sheet 5 INVENTOR CHARLES R; LYON ATTORNEY Patented March 30,1971 6 Sheets-Sheet 4 INVENTOR CHARLES R. LYON ATTORNEY Patentecl' March30, 1971 6 Sheets-Sheet 5 INVENTOR CHARLES R. LYON arrakwsr Pa tent edMarc so, 1971 3,512,595

6 Sheets-Sheet- 6 "we/won CHARLES R. LYON ATTORNEY I A'I'IRI'I'ION MILLThis application is a division of application Ser. No. 436,579, filedMarch 2, 1965, now U.S. Pat. No. 3,406,916.

This invention relates to the attrition of woodpulp for use in theproduction of cellulose derivatives.

In the manufacture of cellulose derivatives it is customary to employ,as one of the starting materials, fibers of bleached woodpulp of highalpha cellulose content (so-called chemical pulp"). The pulp issupplied, by the pulp manufacturer, in

the form of sheet material prepared by drying a wet mass of individualfibers. Before this pulp is converted chemically to the desiredcellulose derivative (e.g. to an ester such as cellulose acetate) it iscommon practice to pass the sheet material to an attrition mill toseparate the individual cellulose fibers, which may for example be onthe order of /s--%-inch in length. One conventional attrition mill usedfor this purpose employs two concentric discs one of which is rotatingat high speed relative to the other, which is usually stationary. Thediscs have opposing teeth which project into the attrition zone, betweenthe discs, and which engage the dry pulp material as it passes throughthis zone. The stationary disc has a central hole through which the pulpsheet material is fed to "the attrition zone, while the rotating disc isprovided with knife elements facing this central hole and arranged in amore or less random pattern; these knife elements serve to cut the pulpmaterial into smaller pieces which are thrown outward eentrifugallythrough the space between the two discs. The resulting individual fiberswhich pass out from the e periphery of the discs are taken up by acurrent of air, produced by the action of a suction fan, and deliveredto a storage zone for conversion into the desired cellulose derivative.1

The pulp sheet material, as furnished by the supplier, generally has awidth of about 2 to 3 feet and a thickness of about one-eighth inch, andis supplied in roll form or in large individual sheets. The feed hole inthe stationary disc of the attrition mill is, for example, about I8inches in diameter. In feeding the sheet material to the attrition mill,it has for many years been the practice for an operator to bend theedges of the sheet material upwardly, pass the material into the largerend of a conical chute leading to the intake opening of the attritionmill, and thereby urge the resulting folded or partially rolled sheetagainst against the knife elements of the rotating disc.

It is an object of this invention to increase the rate of production ofpulp fibers in the attritionmill.

. Another object of this invention is to improve the operation of theattrition mills used for the production of pulp fibers.

Other objects of this invention'will be apparent from the followingdetailed description and claims. In this description and claims, allproportions are by weight unless otherwise indicated.

A device for use in one aspect of this invention is illustrated in theaccompanying drawing in which:

FIG. 1 is a side view showing the attrition mill coupled to a device forsupplying the pulp material thereto;

FIG. 2 is a view taken from the right'end of FIG. I;

' FIG. 3 is a view of the right end of FIG. 1 with portions in crosssection;

FIG. 4 is a view of the right end of FIG. 1 showing the opposite side ofthe pulp-supplying device;

FIG. 5 is a view taken from the same end as in FIG.2 and showingportions in cross section;

FIG. 6 is a cross-sectional view of the pulp-supplying device showingdetails of the construction; and

FIG. 7 is a perspective view of details of hammer elements andsheet-supporting elements.

In the drawing reference numeral 11 (FIG. I) designates an attritionmill of conventional type (Sprout, Waldron) having a casing I12 and apair of opposed toothed discs 13 and 14 (FIG. 3), the stationary disc 13having a central opening 16 and the driven rotating disc 14 havingcutter knife elements 17; the disc 14 is driven by a motor 18, whosedrive shaft 18a is supported on bearings 18b (FIG. 1).

In the embodiment of the invention illustrated in the drawing there ismounted, in position to feed cellulose pulp material 19 (as from a roll19a, FIG. 1) to the inlet opening 16, a combined hammer mill andconveying device, indicated generally as 21, comprising a hammer millportion 22 (FIGS. 3 and 4) mounted on a vertical plate 23 arising from abase 24, which base also supports a conveyor portion 26 located justbelow the hammer mill portion 22.

At the inlet end of the hammer mill portion 22, there is mounted a pairof feed rolls 28, 29 (FIGS. 3 and 4) of sufficient length to accommodatethe full width of the woodpulp sheet material, the lower feed roll 28being suitably driven, as through a belt 31 fitted over a pulley 32 anddriven by an electric motor 33 which may be mounted on the base 24. Theupper feed roll 29, which is an idler roll, is biased downward, in anysuitable fashion, as by a spring or weight (not shown) to press thesheet material, fed to the nip of these two rolls, against the drivenroll 28. Advantageously, the rolls 28 are rubber-covered rolls.

Within the hammer mill portion 22 a series of spaced parallel hammers 36are mounted on, and keyed to, a rotatable hammer shaft 37 which isdriven in any suitable fashion, as by an electric motor 38 supportedatop the hammer mill portion and connected to the hammer shaft 37through a belt 39 engaging a pulley at the end of that shaft. Thehammers 36 have central bearing areas 41 (FIG. 5) projecting on bothsides of each hammer to provide for their rigid support and to act asspacers;

The hammers 36 are adapted to coact, in interfitting relation, with aset of spaced stationary cutter teeth 42 mounted on a stationary bar 43and so positioned thatthe pulp sheet material, as it passes from thefeed rolls, is supported on the cutter teeth and is struck andpenetrated by the downwardly moving hammers, which then pass between thecutter teeth.

The hammers 36 in the embodiment illustrated in the drawing, aretapered, being of parallelogram disposed at about 45 to the other twoedges to fonrr sharp corners and are so mounted that, on rotation of thehammer shaft 37, their long flat edges strike the top of the pulp sheetmaterial. The tapered construction of the hammers provides adequatestrength while limiting the masses of the hammers at their outer edges,thus facilitating high speed rotation of the hammer shaft. Adjacenthammers, although in parallel planes, are mounted'at an angle to eachother; as shown in the drawing this angle is so that alternate hammersare parallel to each other. In one preferred embodiment the hammers 36and the teeth 42 are uniformly spaced and are each about one-half inchwide, with straight flat vertical sides, and the hammertooth clearance,on each side of each hammer, is about onefourth inch.

The action of' the hammers 36 which may be rotated at, for example, 1800r.p.m. with a tip velocity of 4500 feet per minute, breaks the sheetmaterial into more or less rectangular chips or pieces, e.g. /wiinchsquares or Aid-inch rectangles, depending on the relative preset,constant speeds of hammer rotation and of sheet feeding. For bestresults the sheet material being fed is struck by the operative ends ofeach h'ammer no later than it is struck by that portion of the hammerwhich is closer to the center of rotation of the hammer; in this way thepieces of pulp are chipped off from the forward end of the advancingsheet without cutting the sheet material into ribbons.

The chips of sheet material fall between the cutter teeth 42 through thelarge open top of a tapered conveyor housing 46 having a circular bottom47 in which there is mounted a rotatable helical feed screw 48 whoseaxis is concentric with that of the center of the curvature of thecircular bottom 47. The screw 48 is suitably driven, as by an electricmotor at mounted on the base 24 connected to the center shaft 52 of thefeed screw d8 by means of a belt. The chips are delivered, by the actionof the feed screw 48, directly to the inlet 16 of the attrition millIll, which inlet is concentric with the feed screw 48.

it is found that the use of the arrangement described above makes itpossible to triple the maximum practical continuous rate of feed of thesheet material to the attrition mill, without changing the speed ofoperation of the attrition mill, and with the use of substantially lesspower in the mill. The load on the attrition mill is found to be muchmore uniform, the mill operates with little, if any, of the bumping andgrinding observed with the previous method, and maintenance costs areconsiderably reduced. Also, this invention eliminates the difficultiesresulting from breaking of the cutter elements of the rotating disc andthe need to sharpen these elements often. The usual frequentinterruptions of operation due to breaking or tearing of the relativelyweak pulp sheet material as it was fed to the attrition mill are alsoavoided.

In addition the use of this invention has been found to improve theproperties (eg filtration characteristics) of cellulose acetate spinningsolutions produced in conventional manner from the pulp, despite thetripled rate of operation. This effect is observed, for example, insolutions made, in the conventional manner, by acetylating the pulpfibers, ripening the acetylated product to produce secondary celluloseacetate and dissolving this cellulose acetate in acetone to form aviscous spinning solution, or dope, for use in the formation ofcontinuous filaments.

It is to be understood that the foregoing detailed description is givenmerely by way of illustration, and that variations may be made thereinwithout departing from the spirit of out invention.

lclaim:

1. In an apparatus for the separation of fibers of cellulose pulp sheetmaterial which includes an attrition mill having a stationary tootheddisc and opposing rotary toothed disc, said stationary disc having acentral aperture for the reception of said sheet material, theimprovement which comprises means providing an impact zone, a drivenroll extending across the width of said sheet material for continuouslypositively feeding said pulp sheet material in unfolded state to saidimpact zone. a series of spaced tapered parallelogram shaped hammerelements mounted in said impact zone on a driven rotary shaft forhitting said sheet material, adjacent to its leading edge; with repeatedimpacts spaced across the width of said sheet material to break the pulpmaterial at said leading edge into chips, said hammer elements adaptedto coact in interfitting relation with a set of spaced stationarycutter, teeth on a stationary bar, a series of spaced supportingelements, between said hammer elements, for supporting and spacing saidhammer elements, the construction and arrangement being such that thechips fall between the spaced hammer elements, a conveyor mounted belowsaid hammer elements for receiving said chips and for continuouslyfeeding said chips to said aperture.

2. Apparatus as set forth in claim 1 in which said hammer elements areso disposed on said shaft that adjacent elements hit said sheet materialat different times, and said cutter teeth are so disposed in relation tosaid hammer elements that said hammer elements strike said sheetmaterial at points upstream of said leading edge no later than theystrike said edge, and said conveyor is a screw conveyor having an outletdirectly abutting said central aperture.

3. Apparatus as set forth in claim 2 in which said hammer elements areparallelogram-shaped and are mounted on said shaft between theiroperative ends to hit the said sheet material twice with each rotationof said shaft and are tapered toward said ends.

4. Apparatus as set forth in claim 3 in which the parallelogram-shapedhammer elements have two edges of the parallelogram each disposed atabout 45 to one of the other two edges and the hammer elements aremounted so that their long flat edges strike the top of the sheetmaterial.

5. Apparatus as set forth in claim 2 in which adjacent hammer elementsare mounted in parallel planes and said hammer elements are at an angleto each other.

UNITED STATES PATENT OFFICE P0-105U (5/69) CERTIFICATE OF CORRECTIONPatent No. 3,572,595 Dated March 30. 1971 Inventor(s) Charles R. Lyon Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 1, first line, after "of", insert U. S.-

. Column 1, line 29, delete "e" between "the periphery" Column 2, line38, after the word "parallelogram", insert shape, with two of the edgesof the parallelogram-- Column 3, line 27, "out" should be ---our- Signedand sealed this l). .th day of December 1971.

(SEAL) Attest: I

EDWARD M.FLETCHER,JR. Atteating Officer ROBERT GO'ITSCHALK ActingCommissioner of Pete:

1. In an apparatus for the separation of fibers of cellulose pulp sheetmaterial which includes an attrition mill having a stationary tootheddisc and opposing rotary toothed disc, said stationary disc having acentral aperture for the reception of said sheet material, theimprovement which comprises means providing an impact zone, a drivenroll extending across the width of said sheet material for continuouslypositively feeding said pulp sheet material in unfolded state to saidimpact zone, a series of spaced tapered parallelogram shaped hammerelements mounted in said impact zone on a driven rotary shaft forhitting said sheet material, adjacent to its leading edge; with repeatedimpacts spaced across the width of said sheet material to break the pulpmaterial at said leading edge into chips, said hammer elements adaptedto coact in interfitting relation with a set of spaced stationary cutterteeth on a stationary bar, a series of spaced supporting elements,between said hammer elements, for supporting and spacing said hammerelements, the construction and arrangement being such that the chipsfall between the spaced hammer elements, a conveyor mounted below saidhammer elements for receiving said chips and for continuously feedingsaid chips to said aperture.
 2. Apparatus as set forth in claim 1 inwhich said hammer elements are so disposed on said shaft that adjacentelements hit said sheet material at different times, and said cutterteeth are so disposed in relation to said hammer elements that saidhammer elements strike said sheet material at points upstream of saidleading edge no later than they strike said edge, and said conveyor is ascrew conveyor having an outlet directly abutting said central aperture.3. Apparatus as set forth in claim 2 in which said hammer elements areparallelogram-shaped and are mounted on said shaft between theiroperative ends to hit the said sheet material twice with each rotationof said shaft and are tapered toward said ends.
 4. Apparatus as setforth in claim 3 in which the parallelogram-shaped hammer elements havetwo edges of the parallelogram each disposed at about 45* to one of theother two edges and the hammer elements are mounted so that their longflat edges strike the top of the sheet material.
 5. Apparatus as setforth in claim 2 in which adjacent hammer elements are mounted inparallel planes and said hammer elements are at an angle to each other.